Thermal sound generating device

ABSTRACT

A thermoacoustic generating apparatus ( 1 ) is for generating acoustic waves by temperature modulation of solids, and is provided with: a thermoelement layer ( 12 ); a first electrode layer ( 11 ), laminated on one surface of the thermoelement layer; and a second electrode layer ( 13 ), laminated on the other surface of the thermoelement layer.

TECHNICAL FIELD

The present invention relates to, for example, a thermoacousticgenerating apparatus for generating acoustic waves by temperaturemodulation of solids.

BACKGROUND ART

As the thermoacoustic generating apparatus, for example, patentdocuments 1 and 2 disclose such construction that voltage application isrepeated on a resistance heating element and that Joule heat is used totemperature-modulate a thermal layer.

Patent document 1: Japanese Patent Application Laid Open No. Hei3-140100

Patent document 2: Japanese Patent Application Laid Open No. Hei11-300274

Patent document 3: Japanese Patent Application Laid Open No. 2005-150797

DISCLOSURE OF INVENTION Subject to be Solved by the Invention

In such construction that the Joule heat is used for the temperaturemodulation, an acoustic wave signal outputted as a result of thetemperature modulation is on the order of the square of an input signalinputted to control the temperature modulation. This causes such atechnical problem that the acoustic wave signal which is different fromthe input signal is outputted. Thus, as disclosed in a patent document3, such a technology has been suggested that a direct current signal issuperimposed on an alternating current signal to generate an inputsignal and that an acoustic wave signal component with the samefrequency as that of the input signal is outputted.

In this technology, however, it is hardly possible to completelyeliminate a frequency component which is different from that of inputsignal (i.e. a strain component). The strain component can be reduced byincreasing the direct current signal, superimposed on the alternatingcurrent signal, but this significantly reduces the generation efficiencyof the acoustic waves.

On the other hand, the patent document 2 also discloses suchconstruction that a Peltiert element is used as a heating-element thinfilm, in addition to the construction that the Joule heat is used forthe temperature modulation. In the construction disclosed in the patentdocument 2, however, a heat insulating layer is under and in contactwith the heating-element thin film, which is made of the Peltiertelement, and an electric current is not applied to this part fordriving. In this construction, the resistance of the heating-elementthin film increases with respect to the electric current because theelectric current flows in a direction orthogonal to the film thicknessdirection of the heating-element thin film (in other words, horizontallyto the thickness direction or planarly), resulting in a technicalproblem of an increase in the generation of the Joule heat. Theincreased Joule heat regardless of the Peltiert element used as theheating element causes the aforementioned various problems. Moreover,because of a small contact point between the heat-element thin film anda signal terminal, it is hardly possible to obtain a large temperaturechange by a thermoelectric effect.

In view of the aforementioned problems, it is therefore an object of thepresent invention to provide, for example, a thermoacoustic generatingapparatus capable of generating acoustic waves by temperaturemodulation, efficiently, while preventing the generation of Joule heat.

Means for Solving the Subject

The above object of the present invention can be achieved by athermoacoustic generating apparatus, according to claim 1, forgenerating acoustic waves by temperature modulation of solids, providedwith: a thermoelement layer; a first electrode layer, laminated on onesurface of the thermoelement layer; and a second electrode layer,laminated on the other surface of the thermoelement layer locatedopposite to the one surface.

These operation and other advantages of the present invention willbecome more apparent from the embodiments explained below.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view conceptually showing a first basicstructure of a thermoacoustic generating apparatus in an example.

FIG. 2 is a cross sectional view conceptually showing a second basicstructure of the thermoacoustic generating apparatus in the example.

FIG. 3 is a cross sectional view conceptually showing a third basicstructure of the thermoacoustic generating apparatus in the example.

FIG. 4 is a cross sectional view conceptually showing a fourth basicstructure of the thermoacoustic generating apparatus in the example.

FIG. 5 is a cross sectional view conceptually showing a structure of thethermoacoustic generating apparatus with an increased area in which anupper electrode and an ambient gas are in contact.

FIG. 6 is a perspective view conceptually showing a first basicstructure of a thermoacoustic generating apparatus in a first modifiedexample.

FIG. 7 is a perspective view conceptually showing a second structure ofthe thermoacoustic generating apparatus in the first modified example.

FIG. 8 is a perspective view conceptually showing a first basicstructure of a thermoacoustic generating apparatus in a second modifiedexample.

FIG. 9 is a perspective view conceptually showing a second structure ofthe thermoacoustic generating apparatus in the second modified example.

FIG. 10 is a perspective view conceptually showing a first basicstructure of a thermoacoustic generating apparatus in a third modifiedexample.

FIG. 11 is a perspective view conceptually showing a second basicstructure of the thermoacoustic generating apparatus in the thirdmodified example.

FIG. 12 is a perspective view conceptually showing a third structure ofthe thermoacoustic generating apparatus in the third modified example.

FIG. 13 is a perspective view conceptually showing a fourth structure ofthe thermoacoustic generating apparatus in the third modified example.

DESCRIPTION OF REFERENCE CODES

-   1, 100, 101, 102, 103, 104, 105 thermoacoustic generating apparatus-   10 thermoacoustic generating unit-   11 upper electrode-   12 thermoelement-   13 lower electrode-   14 filler-   15 supporting base

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, as the best mode for carrying out the present invention, anexplanation will be given on embodiments of the thermoacousticgenerating apparatus of the present invention.

An embodiment of the thermoacoustic generating apparatus of the presentinvention is a thermoacoustic generating apparatus for generatingacoustic waves by temperature modulation of solids, provided with: athermoelement layer; a first electrode layer, laminated on one surfaceof the thermoelement layer; and a second electrode layer, laminated onthe other surface of the thermoelement layer located opposite to the onesurface.

According to the embodiment of the thermoacoustic generating apparatusof the present invention, it has such a structure that the firstelectrode layer and the second electrode layer sandwich thethermoelement layer therebetween and that the first electrode layer, thethermoelement layer, and the second electrode layer are laminated inthis order.

By applying a voltage between the first electrode layer and the secondelectrode layer, an electric current flows in the thermoelement layer.As a result, heat-generation or heat-absorption occurs in the boundarybetween the first electrode layer and the thermoelemet layer by thethermoelectric effect. In the same manner, the heat-generation or theheat-absorption occurs in the boundary between the second electrodelayer and the thermoelemet layer by the thermoelectric effect. In thiscase, due to the nature of the thermoelement, if the heat-generationoccurs in the boundary between the first electrode layer and thethermoelement layer, the heat-absorption occurs in the boundary betweenthe second electrode layer and the thermoelement layer. On the otherhand, if the heat-absorption occurs in the boundary between the firstelectrode layer and the thermoelement layer, the heat-generation occursin the boundary between the second electrode layer and the thermoelementlayer. This allows the heating or cooling of the first electrode layerand the second electrode layer, resulting in the heating or cooling ofan ambient gas which is in contact with the first electrode layer andthe second electrode layer. At this time, by controlling the voltageapplied between the first electrode layer and the second electrode layer(e.g. by controlling the magnitude, sign, and the like of the voltage),i.e. by controlling the electric current flowing in the thermoelementlayer (e.g. by controlling the magnitude, flowing direction, and thelike of the electric current), it is possible to control the heating andcooling of the ambient gas. As a result, the acoustic waves can begenerated.

In particular, in the embodiment, the first electrode layer, thethermoelement layer, and the second electrode layer have the laminationstructure, and the thermoacoustic generating apparatus is driven byapplying the electric current in direction of the film thickness of thethermoelement layer. Thus, electrical resistance is reduced, to therebylimiting or controlling Joule heat. Moreover, each of the firstelectrode layer and the second electrode layer is in planar contact withthe thermoelement layer, so that the heat-generation and theheat-absorption occur in a larger area. As a result, the heat-generationand the heat-absorption can efficiently occur; namely, the acousticwaves can be generated by temperature modulation, efficiently.

Moreover, according to the embodiment, as described later, theheat-generation and the heat-absorption can occur more efficiently byadjusting the thickness or the like of the first electrode layer and thesecond electrode layer.

Incidentally, in the embodiment, either the heat-generation and theheat-absorption in the first electrode layer or the heat-generation andthe heat-absorption in the second electrode layer may be used togenerate the acoustic waves. However, the heat-generation and theheat-absorption in either the first electrode layer or the secondelectrode layer are preferably used to generate the acoustic waves. Ifthe heat-generation and the heat-absorption in only the first electrodelayer are used to generate the acoustic waves, it is preferablyconstructed such that the heat-generation and the heat-absorption in thesecond electrode layer do not influence on the temperature modulation bythe heat-generation and the heat-absorption in the first electrodelayer. In the same manner, if the heat-generation and theheat-absorption in only the second electrode layer are used to generatethe acoustic waves, it is preferably constructed such that theheat-generation and the heat-absorption in the first electrode layer donot influence on the temperature modulation by the heat-generation andthe heat-absorption in the second electrode layer.

In the embodiment below, an explanation will be given on suchconstruction that the heat-generation and the heat-absorption in thefirst electrode layer are used to efficiently generate the acousticwaves. However, it will be understood that aspects in using theheat-generation and the heat-absorption in the first electrode layer toefficiently generate the acoustic waves, which are described later, maybe applied, as occasion demands, even when the heat-generation and theheat-absorption in the second electrode layer are used to efficientlygenerate the acoustic waves.

In one aspect of the embodiment of the thermoacoustic generatingapparatus of the present invention, a heat capacity of the firstelectrode layer is less than that of the second electrode layer.

According to this aspect, since the heat capacity of the first electrodelayer is less, it is possible to increase a temperature change by theheat-generation and the heat-absorption in the first electrode layer. Onthe other hand, since the heat capacity of the second electrode layer isgreater, it is possible to control or limit a temperature change by theheat-generation and the heat-absorption in the second electrode layer,thereby reducing an influence on the temperature change in the firstelectrode layer.

Incidentally, more preferably, the heat capacity of the first electrodelayer is preferably less than or equal to 1/10 of that of the secondelectrode layer.

In an aspect of the thermoacoustic generating apparatus in which theheat capacity of the first electrode layer is less than that of thesecond electrode layer, as described above, a film thickness of thefirst electrode layer may be thinner than that of the second electrodelayer.

By virtue of such construction, it is possible to make the heat capacityof the first electrode layer less than that of the second electrodelayer, relatively easily, by adjusting the film thickness of each of thefirst electrode layer and the second electrode layer, as occasiondemands.

In an aspect of the thermoacoustic generating apparatus in which theheat capacity of the first electrode layer is less than that of thesecond electrode layer, as described above, a specific heat capacity ofa material that constitutes the first electrode layer may be less thanthat of a material that constitutes the second electrode layer.

By virtue of such construction, it is possible to make the heat capacityof the first electrode layer less than that of the second electrodelayer, relatively easily, by adjusting the material that constitutes thefirst electrode layer and the material that constitutes the secondelectrode layer, as occasion demands.

In an aspect of the thermoacoustic generating apparatus in which theheat capacity of the first electrode layer is less than that of thesecond electrode layer, as described above, one or a plurality of poresmay be formed in the first electrode layers.

By virtue of such construction, it is possible to make the heat capacityof the first electrode layer less than that of the second electrodelayer, relatively easily, by using the first electrode layer in whichthe one or plurality of pores are formed (i.e. the porous firstelectrode layer).

Incidentally, the “pore” in the present invention widely includes, ineffect, a hole which penetrates the first electrode layer, a dent on thesurface of the first electrode layer, and a closed gap or space formedinside the first electrode layer.

In another aspect of the embodiment of the thermoacoustic generatingapparatus of the present invention, a supporting base is provided on thesecond electrode layer surface opposite to a side on which the secondelectrode layer is in contact with the thermoelement layer.

According to this aspect, the first electrode layer and the secondelectrode layer can have substantially the same structure, so that it ispossible to substantially equalize the electrical resistance of thefirst electrode layer and that of the second electrode layer. Thisallows the electric current flowing in the thermoelement layer to have auniform in-plane distribution, resulting in a uniform in-planedistribution in temperature in the first electrode layer. Therefore, itis possible to realize practically extremely useful construction, inthat an in-plane distribution can be uniformed in an acoustic pressuregenerated in the first electrode layer.

Incidentally, in this aspect, the heat capacity of the first electrodelayer is preferably less than the total heat capacity of the secondelectrode layer and the supporting base.

In another aspect of the embodiment of the thermoacoustic generatingapparatus of the present invention, the thermoacoustic generatingapparatus is provided with a plurality of thermoacoustic generatingunits, each provided with the first electrode layer, the thermoelementlayer, and the second electrode layer, and the plurality ofthermoacoustic generating units are electrically connected to each otherto match a direction of a heat flow in all the plurality ofthermoacoustic generating units, the heat flow being generated by anelectric current flowing in the thermoelement layer through the firstelectrode layer and the second electrode layer.

According to this aspect, even if the amount of the heat-generation orthe amount of the heat-absorption generated in one thermoacousticgenerating unit is small with respect to the electric current flowing inthe thermoelement layer, it is possible to increase the amount of theheat-generation or the amount of the heat-absorption generated as theentire thermoacoustic generating apparatus because the plurality ofthermoacoustic generating units are connected. The plurality ofthermoacoustic generating units are also arranged to match the directionof a generated heat flow in all the plurality of thermoacousticgenerating units. More specifically, the plurality of thermoacousticgenerating units are arranged to generate heat, for example, on thefirst electrode layer side, with respect to the electric current in apredetermined direction applied to the electrically connectedthermoacoustic generating units. Thus, the thermoacoustic generatingapparatus can generate the acoustic waves, more preferably.

In an aspect of the thermoacoustic generating apparatus provided withthe plurality of the thermoacoustic generating units, as describedabove, the thermoelement layer provided for each of the plurality ofthermoacoustic generating units may be provided with a thermoelement ofa same conductivity type (e.g. all p-type thermoelements or all n-typethermoelements), and the first electrode layer provided for one of theplurality of thermoacoustic generating units is connected to the secondelectrode layer provided for another one of the plurality ofthermoacoustic generating units that is adjacent to the onethermoacoustic generating unit.

As described above, by connecting the plurality of thermoacousticgenerating units electrically in series, it is possible to match thedirection of the generated heat flow, in all the plurality ofthermoacoustic generating units, which are constructed of the sameconductive type thermoelements, relatively easily.

In an aspect of the thermoacoustic generating apparatus provided withthe plurality of the thermoacoustic generating units, as describedabove, the plurality of thermoacoustic generating units may includefirst thermoacoustic generating units provided with the thermoelementlayer constructed of a p-type thermoelement and second thermoacousticgenerating units provided with the thermoelement layer constructed of anretype thermoelement, the first thermoacoustic generating units and thesecond thermoacoustic generating units may be alternately arranged, andthe first electrode layer provided for one of the plurality of firstthermoacoustic generating units may be connected to the first electrodelayer provided for one of the plurality of second thermoacousticgenerating units that is adjacent to the one first thermoacousticgenerating unit, and the second electrode layer provided for the onesecond thermoacoustic generating unit may be connected to the secondelectrode layer provided for another one of the plurality of firstthermoacoustic generating units that is adjacent to the one secondthermoacoustic generating unit.

As described above, by connecting the plurality of thermoacousticgenerating units electrically in series, it is possible to match thedirection of the generated heat flow, in all the plurality ofthermoacoustic generating units, which are constructed of the differentconductive type thermoelements, relatively easily.

In an aspect of the thermoacoustic generating apparatus provided withthe plurality of the thermoacoustic generating units, as describedabove, a cross section substantially parallel to the first electrodelayer or the second electrode layer in each of the plurality ofthermoacoustic generating units may have a long side and a short side,and the first electrode layer may be connected to the first electrodelayer or second electrode layer provided for another thermoacousticgenerating unit adjacent to the long side.

By virtue of such construction, the electrical resistance of thethermoacoustic generating apparatus is reduced, so that it is possibleto generate the acoustic waves by using the heat-generation and theheat-absorption in the first electrode layer, more efficiently.

In an aspect of the thermoacoustic generating apparatus provided withthe plurality of the thermoacoustic generating units, as describedabove, at least one portion between the plurality of thermoacousticgenerating units (e.g. an entire space between the plurality ofthermoacoustic generating units, a partial space located under the firstelectrode layer of the space between the plurality of thermoacousticgenerating units, or the like) may be filled with a filler havingelectrical insulation.

By virtue of such construction, the filler allows the first electrodelayer, which electrically connects the adjacent thermoacousticgenerating units, to be supported without floating in the air, therebyfurther thinning the first electrode layer. By this, it is possible togenerate the acoustic waves by using the heat-generation and theheat-absorption in the first electrode layer, more efficiently. Even ifthe space is filled with the filler, it is possible to preferablyprevent such a disadvantage that the plurality of thermoacousticgenerating units electrically short-circuit outside of the firstelectrode layer or the second electrode layer, because the filler hasthe electrical insulation.

In an aspect of the thermoacoustic generating apparatus in which thespace is filled with the filler, as described above, the fillerpreferably further has thermal insulation property.

Such construction makes it possible to preferably prevent theheat-generation or the heat-absorption of the first electrode layer fromdiffusing into the second electrode layer.

In another aspect of the thermoacoustic generating apparatus of thepresent invention, surface roughening is performed on the firstelectrode layer surface opposite to a side on which the first electrodelayer is in contact with the thermoelement layer.

By virtue of such construction, it is possible to increase the surfacearea of the first electrode layer which is in contact with the ambientgas. This allows the more efficient heating and cooling of the ambientgas.

Incidentally, the “surface roughening” in the present invention may be aprocess of forming some unevenness on the surface of the first electrodelayer, and it only needs to increase the surface area, compared to thatof the first electrode layer when there is no unevenness on the surfaceof the first electrode layer.

These operation and other advantages of the present invention willbecome more apparent from the examples explained below.

As explained above, according to the embodiment of the thermoacousticgenerating apparatus of the present invention, it is provided with thefirst electrode layer, the thermoelement layer, and the second electrodelayer. Therefore, it is possible to generate the acoustic waves bytemperature modulation, efficiently, while preventing the generation ofJoule heat.

EXAMPLES

Hereinafter, examples of the present invention will be explained withreference to the drawings.

(1) Basic Structure

Firstly, with reference to FIG. 1, an explanation will be given on anexample of the thermoacoustic generating apparatus of the presentinvention. FIG. 1 is a cross sectional view conceptually showing a firstbasic structure of a thermoacoustic generating apparatus 1 in anexample.

As shown in FIG. 1, the thermoacoustic generating apparatus 1 in theexample is provided with an upper electrode 11, which constitutes onespecific example of the “first electrode layer” of the presentinvention; a thermoelement 12, which constitutes one specific example ofthe “thermoelement layer” of the present invention; and a lowerelectrode 13, which constitutes one specific example of the “secondelectrode layer” of the present invention.

The upper electrode 11 is, for example, an electrode made of metal orthe like with a film thickness of d1. More specifically, for example,the upper electrode 11 is formed by laminating gold with a filmthickness of approximately 200 nm and nickel with a film thickness ofapproximately 20 nm such that the nickel is adjacent to thethermoelement 12 and that the gold is in contact with an ambient gas.

The thermoelement 12 is made of a semiconductor having a thermoelectriceffect (e.g. Peltier effect, Seebeck effect, and the like). Morespecifically, the thermoelement 12 is made of, for example, BiSbTe,BiSbTeSe, or the like. For example, the thermoelement 12 is made ofp-type Bi_(0.5)Sb_(1.5)Te₃ or n-type Bi_(1.8)Sb_(0.2)Te_(2.85)Se_(0.15).The material that constitutes the thermoelement 12 is not limited tothese but may be another semiconductor, metal, oxide, and the like whichprovide the thermoelectric effect.

The lower electrode 13 is, for example, an electrode made of metal orthe like with a film thickness of d2 (wherein d2>d1). More specifically,for example, the lower electrode 13 is formed by laminating nickel witha film thickness of approximately 20 nm, gold with a film thickness ofapproximately 200 nm, and copper with a film thickness of 50 μm in thisorder from the closest to the thermoelement 12. The materials thatconstitute the upper electrode 11 and the lower electrode 13 are notlimited to this but may be another metal which provide ohmic contactwith the thermoelement 12.

The thermoacoustic generating apparatus 1 in the example is driven byapplying an input voltage, which is an alternating current voltageaccording to an acoustic wave signal desired to be generated, betweenthe upper electrode 11 and the lower electrode 13.

According to the thermoacoustic generating apparatus 1 having such astructure, the application of an input voltage between the upperelectrode 11 and the lower electrode 13 allows an electric currentaccording to the input voltage to flow in the thermoelement 12. As aresult, heat is generated or absorbed by the thermoelectric effect inthe boundary between the upper electrode 11 and the thermoelement 12. Inthe same manner, heat is generated or absorbed by the thermoelectriceffect in the boundary between the lower electrode 13 and thethermoelement 12.

This allows the heating or cooling of the upper electrode 11, resultingin the heating or cooling of the ambient gas in contact with the upperelectrode 11. As a result, it is possible to generate acoustic wavesaccording to the heating and cooling of the upper electrode 11 (in otherwords, according to the input voltage applied between the upperelectrode 11 and the lower electrode 13); namely, it is possible togenerate acoustic waves by temperature-modulating the thermoelement 12in accordance with the input voltage applied between the upper electrode11 and the lower electrode 13.

Here, due to the nature of the thermoelement 12, if heat is generated inthe boundary between the upper electrode 11 and the thermoelement 12,heat is absorbed in the boundary between the lower electrode 13 and thethermoelement 12 as much as heat generated in the boundary between theupper electrode 11 and the thermoelement 12. On the other hand, if heatis absorbed in the boundary between the upper electrode 11 and thethermoelement 12, heat is generated in the boundary between the lowerelectrode 13 and the thermoelement 12 as much as heat absorbed in theboundary between the upper electrode 11 and the thermoelement 12. Thus,the heating and cooling of the upper electrode 11 are likely canceled bythe heating and cooling of the lower electrode 13. As a result, there isa possibility that it is hardly possible to preferably generate theacoustic waves according to the input voltage. Alternatively, theacoustic waves generated by a temperature change of the lower electrode13 are in antiphase to those on the upper electrode side, so that theacoustic waves generated in the upper electrode 11 are likely canceledby the acoustic waves in antiphase generated in the lower electrode 13.

In order to prevent such a disadvantage, according to the example, thefilm thickness d1 of the upper electrode 11 is less than the filmthickness d2 of the lower electrode 13. This makes the heat capacity ofthe upper electrode 11 less than that of the lower electrode 13. Here,the heat capacity of the upper electrode 11 is preferably less than orequal to about 1/10 of the heat capacity of the lower electrode 13. As aresult, it is possible to reduce the extent of the heating and cooling(specifically, a temperature rising amount and a temperature droppingamount, a temperature rising speed and a temperature dropping speed, andthe like) of the lower electrode 13, with respect to the extent of theheating and cooling of the upper electrode 11. In other words, it ispossible to limit or control the temperature change of the lowerelectrode 13, with respect to the temperature change of the upperelectrode 11. By this, it is possible to preferably prevent such adisadvantage that the temperature change of the upper electrode 11 iscanceled by the temperature change of the lower electrode 13. Thus, itis possible to preferably generate the acoustic waves according to theinput voltage, in the upper electrode 11.

In addition, in the example, the upper electrode 11, the thermoelement12, and the lower electrode 13 have the lamination structure, so theelectric current flows in a direction along the film thickness directionof the thermoelement 12 (specifically, in the vertical direction in FIG.1). Thus, electrical resistance of the thermoelement 12 can be reduced.Thus, Joule loss is reduced, which makes it possible to efficientlygenerate the acoustic waves. Moreover, it is possible to limit aninfluence of Joule heat, which is on the order of the square of an inputsignal, so that it is possible to preferably generate the acoustic wavesfaithful to the input signal.

Moreover, each of the upper electrode 11 and the lower electrode 13 isin contact with the thermoelement 12 in a planarly large contact area,so that heat can be generated and absorbed in a larger area. As aresult, heat can be efficiently generated and absorbed by thethermoelectric effect; namely, it is possible to efficientlytemperature-modulate the upper electrode 11 and to more efficientlygenerate the acoustic waves.

Incidentally, in the thermoacoustic generating apparatus 1 shown in FIG.1, the heat capacity of the upper electrode 11 is less than or equal toabout 1/10 of the heat capacity of the lower electrode 13. However, evenif the heat capacity of the upper electrode 11 is greater than about1/10 of the heat capacity of the lower electrode 13, it is possible toappropriately receive the effect that the acoustic waves according tothe input voltage applied between the upper electrode 11 and the lowerelectrode 13 can be preferably generated in the upper electrode 11.

Moreover, in the thermoacoustic generating apparatus 1 shown in FIG. 1,the heating and/or cooling of the upper electrode 11 is used to generatethe acoustic waves. Instead of the heating and/or cooling of the upperelectrode 11, however, the heating and/or cooling of the lower electrode13 maybe used to generate the acoustic waves. In this case, however, theheat capacity of the lower electrode 13 is preferably less than that ofthe upper electrode 11. For example, the film thickness d2 of the lowerelectrode 13 is preferably thinner than the film thickness d1 of theupper electrode 11.

Moreover, in the thermoacoustic generating apparatus 1 shown in FIG. 1,the heat capacity of the upper electrode 11 is less than that of thelower electrode 13 by making the film thickness d1 of the upperelectrode 11 thinner than the film thickness d2 of the lower electrode13. However, in addition to or instead of making the film thickness d1of the upper electrode 11 thinner than the film thickness d2 of thelower electrode 13, the structures shown in FIG. 2 and FIG. 3 may allowthe heat capacity of the upper electrode 11 to be reduced from the heatcapacity of the lower electrode 13. FIG. 2 is a cross sectional viewconceptually showing a second basic structure of the thermoacousticgenerating apparatus in the example. FIG. 3 is a cross sectional viewconceptually showing a third basic structure of the thermoacousticgenerating apparatus in the example.

As shown in FIG. 2, in a thermoacoustic generating apparatus 1 a, anupper electrode 11 a has a porous structure. More specifically, theupper electrode 11 a has a predetermined gap or space formed therein, adent formed on its surface, or a through hole formed, which penetratesits cross section.

This makes the heat capacity of the upper electrode 11 a less than thatof a lower electrode 13 a. Thus, it is possible to limit or control thetemperature change of the lower electrode 13 a, with respect to thetemperature change of the upper electrode 11 a. By this, it is possibleto preferably prevent such a disadvantage that the temperature change ofthe upper electrode 11 a is canceled by the temperature change of thelower electrode 13 a. Thus, it is possible to preferably generate theacoustic waves according to the input voltage, in the upper electrode 11a.

Incidentally, both the thermoacoustic generating apparatus 1 shown inFIG. 1 and the thermoacoustic generating apparatus 1 a shown in FIG. 2have such construction that the volume of the upper electrode 11 is lessthan that of the lower electrode 13. In other words, the constructionshown in FIG. 1 is FIG. 2 is summarized as follows: it is preferable tomake the volume of the upper electrode 11 less than that of the lowerelectrode 13 in order to make the heat capacity of the upper electrode11 less than that of the lower electrode 13.

As shown in FIG. 3, in a thermoacoustic generating apparatus 1 b, aspecific heat capacity X1 of the material that constitutes an upperelectrode 11 b is less than a specific heat capacity X2 of the materialthat constitutes a lower electrode 13 b.

This makes the heat capacity of the upper electrode 11 b less than thatof the lower electrode 13 b. Thus, it is possible to limit or controlthe temperature change of the lower electrode 13 b, with respect to thetemperature change of the upper electrode 11 b. By this, it is possibleto preferably prevent such a disadvantage that the temperature change ofthe upper electrode 11 b is canceled by the temperature change of thelower electrode 13 b. Thus, it is possible to preferably generate theacoustic waves according to the input voltage, in the upper electrode 11b.

As shown in FIG. 4, in a thermoacoustic generating apparatus 1 c, asupporting base 15 is laminated on a surface opposite to a surface of alower electrode 13 c on which the lower electrode 13 c is in contactwith the thermoelement 12. Moreover, the heat capacity of the upperelectrode 11 c is less than the entire heat capacity of the lowerelectrode 11 c and the supporting base 15.

By this, it is possible to limit or control the temperature change ofthe lower electrode 13 c, with respect to the temperature change of theupper electrode 11 c. By this, it is possible to preferably prevent sucha disadvantage that the temperature change of the upper electrode 11 cis canceled by the temperature change of the lower electrode 13 c. Thus,it is possible to preferably generate the acoustic waves according tothe input voltage, in the upper electrode 11 c.

In addition, the upper electrode 11 c and the lower electrode 13 c canhave substantially the same structure, so that it is possible tosubstantially equalize the electrical resistance of the upper electrode11 c and that of the lower electrode 13 c. This allows the electriccurrent flowing in a thermoelement 12 c to have a uniform in-planedistribution, resulting in a uniform in-plane distribution intemperature in the upper electrode 11 e. Therefore, it is possible torealize practically extremely useful construction, in that an in-planedistribution can be uniformed in an acoustic pressure generated in theupper electrode 11 c.

Incidentally, in the thermoacoustic generating apparatus 1 shown in FIG.1 to FIG. 4, the acoustic waves are generated by using the heatingand/or cooling of the ambient gas, which is in contact with the upperelectrode 11 and which is caused by the heating and/or cooling of theupper electrode 11. Thus, if the contact area between the upperelectrode 11 and the ambient gas is increased, it is possible to furtheraccelerate the heating and cooling of the ambient gas, which is incontact with the upper electrode 11.

As one example for increasing the contact area between the upperelectrode 11 and the ambient gas, for example, a structure shown in FIG.5 is listed. FIG. 5 is a cross sectional view conceptually showing astructure of the thermoacoustic generating apparatus with an increasedarea in which the upper electrode 11 and the ambient gas are in contact.

As shown in FIG. 5, unevenness is formed by performing surfaceroughening on the surface of an upper electrode 11 d of a thermoacousticgenerating apparatus 1 d. This can increases the surface area of theupper electrode 11 d. Therefore, it is possible to increase the contactarea between the upper electrode 11 d and the ambient gas, therebyfurther accelerating the heating and cooling of the ambient gas, whichis in contact with the upper electrode 11. This makes it possible toefficiently generate the acoustic waves according to the input voltage,in the upper electrode 11 d.

Incidentally, as long as the surface area of the upper electrode 11 d(more specifically, the contact area between the upper electrode 11 dand the ambient gas) can be increased, compared to the surface areaunder the assumption that the upper electrode 11 d has a smooth surfacewithout unevenness, a structure other than the unevenness shown in FIG.5 may be formed on the surface of the upper electrode 11 d. For example,the same effect can be obtained by providing the porous structure forthe upper electrode 11 d.

(2) First Modified Example

Next, with reference to FIG. 6 and FIG. 7, an explanation will be givenon a first modified example of the thermoacoustic generating apparatusin the example. FIG. 6 is a perspective view conceptually showing afirst basic structure of a thermoacoustic generating apparatus in thefirst modified example. FIG. 7 is a perspective view conceptuallyshowing a second structure of the thermoacoustic generating apparatus inthe first modified example.

As shown in FIG. 5, a thermoacoustic generating apparatus 100 in thefirst modified example is provided with a plurality of thermoacousticgenerating units 10. Each of the plurality of thermoacoustic generatingunits 10 has substantially the same structure as those of thethermoacoustic generating apparatuses 1 shown in FIG. 1 to FIG. 4 and isprovided with the upper electrode 11, the thermoelement 12, and thelower electrode 13.

In the thermoacoustic generating apparatus 100 in the first modifiedexample, in particular, a p-type thermoelement 12-1 and an n-typethermoelement 12-2 are used as the thermoelement 12. A thermoacousticgenerating unit 10 provided with the p-type thermoelement 12-1(hereinafter referred to as a “p-type thermoacoustic generating unit10-1” as occasion demands) and a thermoacoustic generating unit 10provided with the n-type thermoelement 12-2 (hereinafter referred to asan “n-type thermoacoustic generating unit 10-2” as occasion demands) arearranged to match the direction of the heat-generation and theheat-absorption in each of the plurality of thermoacoustic generatingapparatuses 10, with respect to the application of the input voltage.More specifically, the plurality of thermoacoustic generatingapparatuses 10 are arranged such that if the upper electrodes 11 of thep-type thermoacoustic generating units 10-1 are heated, the upperelectrodes 11 of the n-type thermoacoustic generating units 10-2 arealso heated. In the same manner, the plurality of thermoacousticgenerating units 10 are arranged such that if the upper electrodes 11 ofthe p-type thermoacoustic generating unit 10-1 are cooled, the upperelectrodes 11 of the n-type thermoacoustic generating units 10-2 arealso cooled.

Here, the upper electrode 11 of the p-type thermoacoustic generatingunit 10-1 and the upper electrode 11 of the adjacent n-typethermoacoustic generating unit 10-2 are unified. In the same manner, thelower electrode 13 of the p-type thermoacoustic generating unit 10-1 andthe lower electrode 13 of another adjacent n-type thermoacousticgenerating unit 10-2 are unified. In other words, a plurality of p-typethermoacoustic generating units 10-1 and a plurality of n-typethermoacoustic generating units 10-2 are alternately connected to beelectrically in series.

Here, the p-type thermoacoustic generating unit 10-1, provided with theupper electrode 11 and the lower electrode 13 with a Peltier constantπ_(m) and the p-type thermoelement 12-1 with a Peltier constant π_(p),provides the amount of the heat-absorption Q_(p)=(π_(p)−π_(m))×I when anelectric current I is applied from the upper electrode 11 to the lowerelectrode 13. In the same manner, the p-type thermoacoustic generatingunit 10-1 provides the amount of the heat-generationQ_(p)=(π_(p)−π_(m))×I when the electric current I is applied from thelower electrode 13 to the upper electrode 11. On the other hand, then-type thermoacoustic generating unit 10-2, provided with the upperelectrode 11 and the lower electrode 13 with a Peltier constant π_(m)and the n-type thermoelement 12-1 with a Peltier constant π_(n),provides the amount of the heat-absorption Q_(n)=(π_(n)+π_(m))×I whenthe electric current I is applied from the lower electrode 13 to theupper electrode 11. In the same manner, the n-type thermoacousticgenerating unit 10-2 provides the amount of the heat-generationQ_(n)=(π_(n)+π_(m))×I when the electric current I is applied from theupper electrode 11 to the lower electrode 13.

Therefore, the amount of the heat-absorption and the heat-generation byone pair of the p-type thermoacoustic generating unit 10-1 and then-type thermoacoustic generating unit 10-2 isQ=Q_(p)+Q_(n)=(π_(p)+π_(n))×I. Thus, if m (wherein m is an integer of 1or more) pairs of the p-type thermoacoustic generating units 10-1 andthe n-type thermoacoustic generating units 10-2 are connected, theamount of the heat-absorption and the heat-generation of the entirethermoacoustic generating apparatus 100 isQ_(total)=m×Q=m×(π_(p)+π_(n))×I.

As described above, by connecting the plurality of thermoacousticgenerating units 10 in series, it is possible to increase the amount ofthe heat-generation or the amount of the heat-absorption to be generatedby the entire thermoacoustic generating apparatus 100. Thus, thethermoacoustic generating apparatus 100 can generate the acoustic wavesfaithful to the input signals, more preferably.

Incidentally, in the example shown in FIG. 6, the upper electrode 11connects the p-type thermoelement 12-1 and the n-type thermoelement 12-2without any support in its one portion. In other words, the upperelectrode 11 is supported by the p-type thermoelement 12-1 and then-type thermoelement 12-2 on the start edge and the end edge but is notsupported in the intermediate part. In this case, it is hard to thin theupper electrode 11, as described in FIG. 1 or the like.

Thus, as in a thermoacoustic generating apparatus 101 shown in FIG. 7,the space that is between the p-type thermoelement 12-1 and the n-typethermoelement 12-2 and that is located under the upper electrode 11 ispreferably filled with a filler 14 having electrical insulation.

This makes it possible to preferably support the upper electrode 11 evenif the film thickness thereof is thinned. Moreover, even if the space isfilled with the filler 14, it is possible to preferably prevent such adisadvantage that the p-type thermoacoustic generating unit 10-1 and then-type thermoacoustic generating unit 10-2 electrically short-circuitoutside of the upper electrode 11 or the lower electrode 13, because thefiller 14 has the electrical insulation.

In order to increase the mechanical strength of the entirethermoacoustic generating apparatus 100, all between the thermoelementsmay be filled with the filler 14 having the electrical insulation.

Incidentally, the filler 14 is more preferably provided with thermalinsulation, in addition to the electrical insulation. This makes itpossible to preferably prevent the heat-generation or theheat-absorption of the upper electrodes 11 from diffusing into the lowerelectrodes 13.

(3) Second Modified Example

Next, with reference to FIG. 8 and FIG. 9, an explanation will be givenon a second modified example of the thermoacoustic generating apparatusin the example. FIG. 8 is a perspective view conceptually showing afirst basic structure of a thermoacoustic generating apparatus in thesecond modified example. FIG. 9 is a perspective view conceptuallyshowing a second structure of the thermoacoustic generating apparatus inthe second modified example.

As shown in FIG. 8, a thermoacoustic generating apparatus 102 in thesecond modified example is provided with the plurality of thermoacousticgenerating units 10, as in the thermoacoustic generating apparatus 100in the first modified example.

In the thermoacoustic generating apparatus 102 in the second modifiedexample, only the p-type thermoelements 12-1 are used as thethermoelements 12. The plurality of p-type thermoacoustic generatingunits 10 are connected electrically in series to match the direction ofa heat flow caused by the application of the electric current.Specifically, as shown in FIG. 8, the plurality of p-type thermoacousticgenerating units 10 are arranged in a matrix, and the upper electrode 11provided for the p-type thermoacoustic generating unit 10-1 is connectedto the lower electrode 13 of the adjacent p-type thermoacousticgenerating unit 10-1.

This allows the thermoacoustic generating apparatus 102 in the secondmodified example to receive the same effect as that received by thethermoacoustic generating apparatus 100 in the first modified example.More specifically, by connecting the plurality of p-type thermoacousticgenerating units 10-1 in series, it is possible to increase the amountof the heat-generation or the amount of the heat-absorption to begenerated by the entire thermoacoustic generating apparatus 102. Thus,the thermoacoustic generating apparatus 102 can generate the acousticwaves faithful to the input signals, more preferably.

Incidentally, FIG. 8 explains the example in which the plurality ofp-type thermoacoustic generating units 10-1 are connected electricallyin series; however, it will be understood that the plurality of n-typethermoacoustic generating units 10-2 may be used instead of theplurality of p-type thermoacoustic generating units 10-1.

In addition, even in the second modified example, as in a thermoacousticgenerating apparatus 103 shown in FIG. 9, the space that is between theadjacent two of the plurality of p-type thermoelements 12-1 and that islocated under the upper electrode 11 is preferably filled with thefiller 14 having electrical insulation.

(4) Third Modified Example

Next, with reference to FIG. 10 to FIG. 13, an explanation will be givenon a third modified example of the thermoacoustic generating apparatusin the example. FIG. 10 is a perspective view conceptually showing afirst basic structure of a thermoacoustic generating apparatus in thethird modified example. FIG. 11 is a perspective view conceptuallyshowing a second basic structure of the thermoacoustic generatingapparatus in the third modified example. FIG. 12 is a perspective viewconceptually showing a third basic structure of the thermoacousticgenerating apparatus in the third modified example. FIG. 13 is aperspective view conceptually showing a fourth structure of thethermoacoustic generating apparatus in the third modified example.

As shown in FIG. 10, in a thermoacoustic generating apparatus 104 in thethird modified example, as in the thermoacoustic generating apparatus100 in the first modified example, the p-type thermoacoustic generatingunits 10-1 and the n-type thermoacoustic generating units 10-2 arearranged to match the direction of the heat flow in each of theplurality of thermoacoustic generating units 10, caused by theapplication of the electric current.

In the thermoacoustic generating apparatus 104 in the third modifiedexample, in particular, a cross section substantially parallel to theupper electrode 11 or the lower electrode 13 of the thermoelement 12 hasa rectangular shape having the long side and the short side. All theupper electrodes 11 connect the p-type thermoelements 12-1 and then-type thermoelements 12-2 which are adjacent on the long side. Thep-type thermoelements 12-1 and the n-type thermoelements 12-2 which areadjacent on the short side are electrically connected by the lowerelectrodes 13.

This allows the thermoacoustic generating apparatus 104 in the thirdmodified example to receive the same effect as that received by thethermoacoustic generating apparatus 100 in the first modified example.More specifically, by connecting the plurality of p-type thermoacousticgenerating units 10 in series, it is possible to increase the amount ofthe heat-generation or the amount of the heat-absorption to be generatedby the entire thermoacoustic generating apparatus 104. Thus, thethermoacoustic generating apparatus 104 can generate the acoustic wavesfaithful to the input signals, more preferably.

Moreover, it is possible to further limit or control the generation ofJoule loss in the upper electrodes 11 and the lower electrodes 13. Inaddition, since the distribution of the electric current flowing in eachof the thermoelements 12 can be relatively reduced, it is possible touniform the in-plane distribution in the acoustic waves generated in theupper electrodes 11.

As shown in FIG. 11, in a thermoacoustic generating apparatus 105 in thethird modified example, as in the thermoacoustic generating apparatus100 in the first modified example, the p-type thermoacoustic generatingunits 10-1 are arranged to match the direction of the heat flow in eachof the plurality of thermoacoustic generating units 10, caused by theapplication of the electric current.

In the thermoacoustic generating apparatus 105 in the third modifiedexample, in particular, as in the thermoacoustic generating apparatus104, the cross section substantially parallel to the upper electrode 11or the lower electrode 13 of the thermoelement 12 has a rectangularshape having the long side and the short side. Moreover, the electricalconnection of the p-type thermoelements 12-1 adjacent on the long sideas shown in FIG. 11 is performed by connecting the upper electrode ofone of the p-type thermoelements 12-1 and the lower electrode 13 of theother p-type thermoelement 12-1. The connection is performed such thatall the p-type thermoacoustic generating units 10-1 are electrically inseries.

This allows the thermoacoustic generating apparatus 105 in the thirdmodified example to receive the same effect as that received by thethermoacoustic generating apparatus 100 in the first modified example.More specifically, by connecting the plurality of p-type thermoacousticgenerating units 10 in series, it is possible to increase the amount ofthe heat-generation or the amount of the heat-absorption to be generatedby the entire thermoacoustic generating apparatus 105. Thus, thethermoacoustic generating apparatus 105 can generate the acoustic wavesfaithful to the input signals, more preferably.

It is also possible to further limit or control the generation of Jouleloss in the upper electrodes 11 and the lower electrodes 13. Inaddition, since the distribution of the electric current flowing in eachof the thermoelements 12 can be relatively reduced, it is possible touniform the in-plane distribution in the acoustic waves generated in theupper electrodes 11.

Incidentally, even in the thermoacoustic generating apparatus 104 in thethird modified example, as in a thermoacoustic generating apparatus 106shown in FIG. 12, the space that is between the p-type thermoelement12-1 and the n-type thermoelement 12-2 and that is located under theupper electrode 11 is preferably filled with the filler 14 having theelectrical insulation. In the same manner, even in the thermoacousticgenerating apparatus 105 in the third modified example, as in athermoacoustic generating apparatus 107 shown in FIG. 13, the space thatis between adjacent two of the plurality of p-type thermoelements 12-1and that is located under the upper electrode 11 is preferably filledwith the filler 14 having the electrical insulation.

Moreover, in order to increase the mechanical strength of the entirethermoacoustic generating apparatus 106 or 107, all between thethermoelements may be filled with the filler 14 having the electricalinsulation.

Furthermore, the thermoacoustic generating apparatuses 1 and the likeexplained with reference to FIG. 1 to FIG. 13, for example, canreproduce music by applying the apparatuses to speakers, or can generateultrasonic waves by applying the apparatuses to ultrasonic-wavegenerators.

The present invention is not limited to the aforementioned example, butvarious changes may be made, if desired, without departing from theessence or spirit of the invention which can be read from the claims andthe entire specification. A thermoacoustic generating apparatus, whichinvolves such changes, is also intended to be within the technical scopeof the present invention.

1. A thermoacoustic generating apparatus for generating acoustic waves by temperature modulation of solids, comprising: a thermoelement layer; a first electrode layer, laminated on one surface of said thermoelement layer; and a second electrode layer, laminated on the other surface of said thermoelement layer located opposite to the one surface, wherein a heat capacity of said first electrode layer is less than or equal to 1/10 of that of said second electrode layer.
 2. The thermoacoustic generating apparatus according to claim 1, wherein a film thickness of said first electrode layer is thinner than that of said second electrode layer.
 3. The thermoacoustic generating apparatus according to claim 1, wherein a specific heat capacity of a material that constitutes said first electrode layer is less than that of a material that constitutes said second electrode layer.
 4. The thermoacoustic generating apparatus according to claim 1, wherein one or a plurality of pores are formed in said first electrode layer so that a volume of said first electrode layer is less than that of said second electrode layer.
 5. The thermoacoustic generating apparatus according to claim 1, wherein a supporting base is provided on the second electrode layer surface opposite to a side on which said second electrode layer is in contact with said thermoelement layer, wherein a heat capacity of the first electrode layer is less than a total heat capacity of the second electrode layer and the supporting base.
 6. The thermoacoustic generating apparatus according to claim 1, wherein said thermoacoustic generating apparatus comprises a plurality of thermoacoustic generating units, each comprising said first electrode layer, said thermoelement layer, and said second electrode layer, and the plurality of thermoacoustic generating units are electrically connected to each other to match a direction of a heat flow in all the plurality of thermoacoustic generating units, the heat flow being generated by an electric current flowing in said thermoelement layer through said first electrode layer and said second electrode layer.
 7. The thermoacoustic generating apparatus according to claim 6, wherein a cross section substantially parallel to said first electrode layer or said second electrode layer in each of the plurality of thermoacoustic generating units has a long side and a short side, and said first electrode layer is connected to said first electrode layer or second electrode layer provided for another thermoacoustic generating unit adjacent to the long side.
 8. The thermoacoustic generating apparatus according to claim 6, wherein said thermoelement layer provided for each of the plurality of thermoacoustic generating units comprises a thermoelement of a same conductivity type, and said first electrode layer provided for one of the plurality of thermoacoustic generating units is connected to said second electrode layer provided for another one of the plurality of thermoacoustic generating units that is adjacent to the one thermoacoustic generating unit.
 9. The thermoacoustic generating apparatus according to claim 6, wherein the plurality of thermoacoustic generating units include first thermoacoustic generating units comprising said thermoelement layer constructed of a p-type thermoelement and second thermoacoustic generating units comprising said thermoelement layer constructed of an n-type thermoelement, the first thermoacoustic generating units and the second thermoacoustic generating units are alternately arranged, and said first electrode layer provided for one of the plurality of first thermoacoustic generating units is connected to said first electrode layer provided for one of the plurality of second thermoacoustic generating units that is adjacent to the one first thermoacoustic generating unit, and said second electrode layer provided for the one second thermoacoustic generating unit is connected to said second electrode layer provided for another one of the plurality of first thermoacoustic generating units that is adjacent to the one second thermoacoustic generating unit.
 10. The thermoacoustic generating apparatus according to claim 6, wherein at least one portion between the plurality of thermoacoustic generating units is filled with a filler having electrical insulation property.
 11. The thermoacoustic generating apparatus according to claim 10, wherein the filler further has thermal insulation.
 12. The thermoacoustic generating apparatus according to claim 1, wherein surface roughening is performed on the first electrode layer surface opposite to a side on which said first electrode layer is in contact with said thermoelement layer. 